Take tea with parasites from a ceremonial cup (7)
I believe the answer is:
chalice
'cup' is the definition.
(chalice is a kind of cup)
'take tea with parasites from a ceremonial' is the wordplay.
I cannot really see how this works, but
'tea' could be 'cha' (cha is a type of tea) and 'cha' is found within the answer.
'parasites' could be 'lice' (lice are parasitic insects) and 'lice' is found within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for chalice that I've seen before include "Large goblet for consecrated wine" , "Communion cup" , "Necessity for communion" , "cup used in company with host" , "Wine cup used at Christian Eucharist" .)